Percussion tool



- v Sept. l0, 1946. R GQ|TD5HM|DT 2,407,604

PERCUSSION TooL Fi'iedFeb. 16, 1944 2 sheets-sheet 1 l l Arron/vir Sept-10, 1946- R. GoLDscHMlDT 2,407,604

PERCUSSION TOOL Filed Feb. 16, 1944 2 Sheets-Sheet 2 Fig. 7i Pig. 9.

A fra .I f I di* v A ArroR/vfr Patented Sept 10, 1946 PERCUSSION kTOOLRudolph Goldschmidt, Sheffield, England Application February 16, 1944,Serial No. 522,681 In Great Britain March 5, 1943 '14 Claims. 1

This invention relates to mechanically-operated percussion tools, suchfor example as power hammers, riveters and paving-breakers.

An object of this invention is to provide a percussion tool which isrelatively light and compact and which .is economical in powerconsumption.

A vfurther object is to provide such a tool which can be readilydesigned to give blows of any desired frequency and energy.

Another object is to provide an electricallyoperated tool having theabove-mentioned advantages.

Another object is to .enable a percussion .tool to be operated b-y ahigh-speed rotary motor without reduction gearing.

Another object `is to enable a percussion tool, such as a riveter, whichis intended forintermittent use, to store during .an idle period kineticenergy which is usefully employed during the subsequent working period.

Further objects and features of the invention will be apparent from thefollowing description of an example thereof as applied to a hand tooland given with reference to the accompanying diagrammatic drawings, `inwhich:

Fig. 1 is a longitudinal section through the tool,

Fig. 2 is a section on the line 2-2 in Fig. 1J

Fig. 3 is an elevation of a detail, as viewed in the plane of Fig. 1,

Figs. 4 and 5 show respectively two alternative forms of this detail,

Fig. 6 is a section on the line B-B in Fig. 1, i

Fig. 7 is an explanatory diagram,

Fig. 8 is a section on the line 8--8 in Fig. 1,

Figs. 9, 10 and 11 are respectively sections .on

the lines 9 9, lil-ID and II-II in Fig. 8,

Fig. 12 is an explanatory diagram, and

Fig. 13 is a section on the line I 3--l3 in Fig. 12.

Referring to Figs. 1, 2 and 3, the tool includes a tubular body 20, anelectric motor 2i fixed to a ange 22 at the outer end of the body, and atool-bit holder 23 slidably guided in an .inner end cap 24 of the bodyfor limited movement along the axis of the motor shaft 25. A strikerincludes a flywheel 26 which is slidably engaged with a splinedextension 25A of the motor shaft. An extension 27 of the tool-bit holder23 is provided with a journal 28 slidably tted in a bore 29 in the lowerend of theshaft 25A in such a manner as to permit the longitudinalmovement of the tool-bit holder. In the periphery of the striker are twodiametrically-opposed pockets 30 each accommodating a hardened steelroller 3i which has two co-axial pins 32 guided in radial slots 33 inthe striker; the roller is thus constrained to be carried round and movelongitudinally with the striker, but is free to move radially withrespect to the striker under the influence of centrifugal force, whileits axis is kept parallel to that of the motor shaft |by the restraintafforded by the surfaces of the pockets in which the grooves 33 areformed; The extent of the radial movement of the rollers is determinedby the ,inner surface of the ybody, on which circumferentially yridgedportions 3B ofthem bear continuously while the tool is operating; Y I

The outer end portion of the body (i. e. the end portion `remote fromthe tool-bit holder 23) contains a nrst race 35 of truncated conicalform disposed with its smaller end adjacent to the motor. When thestriker is rotating within the smaller end of the race 35, the radialthrust of the rollers 3l causes a reactionv which accelerates thestriker inwards towards the tool-bit holder. The lower end face oi thestriker may -be convex at 36 to cao-operate with a concave annularsurface 31 fonthe tool-bit holder.

Immediately adjacent to the larger end of the iirst race 35 is a secondrace 38, the object of 25 which Vis -to impart to the striker, after itsimpact with the tool-bit holdenan ac-celeration in the outward directionsuiicient ot return it to the smaller end of the first race, whilecausing only a relatively slight retardation of` the inwardv movement`of the striker as it passes through the second race towards the end ofits in-stroke. With this object in View, the second race is providedwith two diametri'cally opposed helical paths of such asection that inany plane normal to the axis of the motor shaft this race, which willhereinafter be termed the dynamic screw, everywhere presents a concavesurface to the rollers, which is the condition determining continuouscontact between the rollers and the dynamic screw.

The preferred cross section of the dynamic screw varies from a circleadjacent to and registering exactly with the larger end of the race 35,through ovals (e. g. Fig. 6), of more or less elliptical form, havingthe same major axis and minor axes which progressively decreasetowardsvthe inner end of the dynamic screw. The major axis of the ovalat any section is angularly displaced about the axis of the motor shaft,in the direction opposite to the direction of rotation of this shaft,with respect to the major axis of the oval at any section nearer theouter end of the dynamic screw, so that the hand of the helical pathsdefined by the parts of successive ovals adjacent to the ends of theirmajor axes is opposite to the the striker inwards.

' `between the limits i and ,32 (which maybe for example 7 and 9respectively), so that the grooved paths Ibecome progressively widertowards the outer end of the dynamic screw, whileV the height of thelands between the grooved pathsY decreases towards the outer end owingto the merging of these paths into each other. screw can be machined ona screw-cutting lathe Such a has spent its axial momentum in the blowupon the tool-bit holder, and even if there is no recoil from thelatter, the dynamic coupling between the striker and the screw increasesto a value such that the screw is eective in accelerating the strikeroutwards in readiness for another cycle.

This effect will be explained with reference to on the inner side ofthis groove.

Figs. 12 and 13. In the development of the screw shown in Fig. 12, lineG denotes the bottom of a groove, and line R the top of the dividingridge For the sake of simplicity the slope S between the lines G andhaving a milling attachment, with the aid ois' 7 milling cutter having asuitably profiled periphery and employed to cut in succession theseveral grooves of thesaid family forming each path. Y

At the inner end of the dynamic screw 38 there is preferably a shortrace 39 the bore of which has an oval section which is the same as thesection of the inner end of the dynamic screw 38 but which is nothelical. The major axes of these two sections are relatively displacedthrough a small angle,v e. g. 15 as shown in Fig. 8 (where for the sakeof clearnes's the ovals are 'shown in exaggerated form), while theadjacent edges of the two parts 38 and 39 are rounded, as shown in Figs.9, 10 and 11. The race 39 is provided with a y circumferential groove49.

The races 35 and 39 and the dynamic screw 38 are locked in the tubularbody 20 of the tool by means of an externally*screw-threaded ring 4|engaged in the end ofthe body and bearing against a flanged portion 42of the inner end cap 24, which in turn Vbears against the race 39. Theraces, the dynamic/screw and the rollers 3| are hardened and ground to ahigh surface finish.

The tool-bit holder 23 is associated with a spring 43 compressed betweenthe end of a counf terbore 44 in the end cap 24 anda guide ring 45retained by a snapring 46y engaged on thetoolbit holder which is therebyresiliently biased tolwards the position shown.

The operation of the tool will now be described, starting from thecondition in which the striker 26 is being rotated at normal speed inthe direction ofthe arrow in Fig. 1 and is within the upper part of therace 35. The rollers 34 rotating with the striker are urged radiallyoutwards by centrifugal force and co-operate with the diverging race 35.'Ihe axial components of the forces acting between the race and thelrollers accelerate of the rollers are of smoothly curved profile, therelis only a very loose dynamic coupling between the striker and the screwand the retardation of the inward movement of the striker is relativelyslight,

The tool bit being in contact with work, the

tool-bit holder will be raised to a position such that its surface 31 isagainst the inner end of the shaft A, Consequently the striker willstrikeV the tool-bit holder while the rollers3| are engaged in thedynamic screw. When. the striker YPi. willV be regarded as having theuniform gradient 1i4 (Fig. 13). The roller 3l contacts the dynamic screwat the bottom of the groove at the point A in Fig.l 12 and passes ontothe slope S. A centrifugal force E' urges the roller 3| radiallyoutwards against the slope S, and the axial component C=F tan qi, of theforce acting between the roller and the screw accelerates the strikeroutwards so that the roller describes a path P. If no is the velocity ofwhirl ofthe point of contact between roller and slope S, the finaltranslatory velocity outwards attained at the intersection of lines Gand P is 11:00 tan 2, friction being neglected. It is usually preferablet0 arrange that the path P shall, as shown, leave the slope S at itsouter edge; thoughV in some circumstances the path P may cross the ridgeR and enter the next succeeding helical groove.

The translatory velocity so imparted to the striker is sufficient toreturn it to the race 35, the tapered surface of which constrains therollers to move inwards against the centrifugal forces acting on themand thus arrests the translatory part of the motion of the striker.Thereafter the rollers, continuing to press upon the conical surface ofthe race, Vcooperate with the latter Yto force the striker out again sothat the striker leaves the race 35 with a translatory velocity which,if friction is neglected, will be equal to that with which it enteredthe race 35. Thus the cycle will repeat automatically. Y

The race 38 forms a starting and idling zone for the rollers 3|, inwhich thev striker can be brought up to normal speed when the motor isswitched on and before the tool is set to work. The groove 40 forms atrack round which the rollers can run idly. When the tool is set to workafter the motor has run up to speed, outward movement of the tool-bitholder 23 as the tool is engaged with the work causes the striker to bedisplaced outwards until the ridged portions 34 of the rollers engagethe sinuous groove formed by the roundededges of the race 39 and thedynamic screw, as shown in Figs. 9, 10 and 11. This sinuous grooveoperates to project the striker into the dynamic screw in such a waythat the ridged portions of th'e rollers enter the helical paths atspots so selected that the points of contact between the rollers and therace willfollow substantially the ideal path P (Fig. 12).

The frequency of the movement of the striker is controllable by varyingits total weight, the weight and profile of the rollers, the dimensionsof the race 35 and the pitch and form of the dynamic screw; and thisfrequency can easily be made a small fraction ofthe speed of revolutionof the motor, which may be as high as 10,000 R.. P. M. in a hand tool.

In intermittent service, such as riveting, the motor may be allowed torun continuously, since the power consumption is low while' the tool isidling. During idleintervals the motor speed may be allowed to rise, andthe energy thereby stored in the rotary masses is usefully employed inthe nekty working periodas the motorspeed drops' with increasing load.This possibility of energy storage enables a small and light motor to beused. A motor having a drooping torquespeed characteristic, e. g. aseries motor, is particularly suitable for this application.

The mechanical parts can be kept well lubricated by splash byintroducing a small quantity of oil within the tubular body 2B, which isof oil-tight construction.

Figs. 4 and 5 show two alternative forms of striker. In Fig. 4 therollers 31A are rotatable in hollow rectangular carrier blocks il whichare slidably guided in pockets 30A in the striker 26A. In Fig. 5 ballsSEB are provided instead of rollers and are a working fit in pockets SEBin th'e striker 25B. Rollers are generally preferable, sincev theirprofile can be adapted to design requirements, whereas the radius ofballs is iiXed by the mass desired.

I claim:

1. A percussion tool including a rotary driving member, a divergingtubular race co-aXial with said driving member, a second tubular raceadjacent to the larger end of said diverging race and having helicalpaths on its interior surface, a striker co-aXial with and constrainedto rotate with said driving member and reciprocable along said axis,said striker having centrifugalmasses constrained to rotate with it andcapable of co-operating with said helical paths for transforming thekinetic `energy of rotation of said striker into striking energy oftranslation of said striker, and van abutment member capable ofarresting such translatory movement of said striker while said strikeris within said second race, said helical paths being of opposite hand tothe helixes traced out by said masses during the translatory movement ofsaid striker towards said abutment member.

2. A percussion tool including a rotary driving shaft, a tubular body, astriker connected for rotation with said shaft and capable ofreciproeating longitudinally within said body along the axis of saidshaft into engagement with a tool bit holder slidably mounted in theinner end of 'said body, said striker having a plurality of centrifugalmasses uniformly distributed around it and constrained to rotate andreciprocate with it, but capable of moving at least in part radiallywith respect to th`e striker, the interior surface 'of said body formingnear its outer end a race for said masses, which diverges in the inwarddirection for the purpose of accelerating the striker on its iii-stroke,the interior surface of said body forming beyond the inner end of saiddiverging race a second race providing helical paths for influencing themotion of said masses for the purpose of accelerating the striker on itsout stroke, and the hand of said helical paths being opposite to thehand of the helixes traced out by said masses during the in-stroke ofthe striker.

3. A percussion tool including a rotary driving member, a strikerco-axial with and constrained to Vrotate with said driving member andreciprocable along the axis of rotation of said member, a tubular raceco-aXial with said driving member and having helical paths on itsinterior surface, said striker comprising centrifugal masses constrainedto rotate and reciprocate with it and capable of moving at least in partradially with respect to said axis while co-operating with said interiorsurface, an abutment member positioned to be struck by saidstriker atthe end of its stroke in which the h'and of the helixes traced out bysaid masses is opposite to the hand of said helical path, and meansforreversing the direction of translation of said striker at the otherend of itsstroke, the shape of said interior surface being such as toimpose on said masses when in Contact with .every point on said surfacean acceleration having a component towards said axis, irrespective ofthe axial velocity of said striker. A

4. A percussion tool including a rotary driving member, a strikerco-aXial with and 'constrained to rotate with said driving member andreciprocable along the axis of rotation of said member, a tubular raceco-aXial with said driving member and having helical'fpaths on itsYinterior surface, said striker carrying centrifugal rolling elementsconstrained to rotate and reciprocate therewith and capable of moving atleast in part radially with respect to said axis while rolling roundsaid interior surface, an abutment member positioned to be struck bysaid striker atl the end of its stroke in which the hand of the heliXestraced out by said masses is opposite to the hand of said helical paths,and means for reversing th'e direction of translation of said striker atthe other end of its stroke, the shape of said interior surface and ofsaid rolling elements being such as to impose on said rolling elementswhen` in contact with every point on said surface an acceleration havinga component towards said axis, irrespective of the axial velocity ofsaid striker.

5. A percussion tool including a rotary driving member, a divergingtubular race co-aXial with said driving member, a second tubular raceadjacent to the larger end of said diverging race and having helicalpaths on its interior surface, a striker co-aXial with and constrainedto rotate with said driving member and reciprocable along said axis,said striker having centrifugal rollers constrained to rotate andreciprocate with it while rolling round the interior surfaces of saidraces, said rollers co-operating with said helical paths fortransforming the kinetic energy of rotation of said striker intostriking energy of translation of said striker, and an abutment membercapable of arresting `such translatory movement of said striker whilesaid striker is within said second race, said helical paths being ofopposite hand to the helixes traced out by said rollers during thestroke of said striker towards said abutment.V

6. A percussion tool including a tubular body, lan electric motor at oneend of and co-axial with said body, a tool-bit holder slidably mountedco- Xially with and in the other end of said body, said motor having ashaft extending co-aXially within said body, a bearing between the endof said shaft and said toolbi`t holder, a striker mounted on andconstrained to rotate with said shaft and reciprocable within said bodyfor cooperation with said tool-bit holder, said striker havingcentrifugal masses constrained to rotate with it and movable at least inpart radially with respect to said axis while co-operating with theinterior surface of said body, said interior surface having grcovedhelical paths in the portion thereof that cci-operates with said masseswhen said striker is impacting said tool-bit holder, the hand of saidhelical paths being opposite to that of the paths traced by said masseswhile said striker approaches said tool-bit holder, and means forreversing the direction of the translatory motion Cf said striker whileit is in the neighborhood of the' end of said bodyadjacent Vto saidmotor and thereby returning saidv striker into said grooved portion.

7. A percussion tool including a tubular body, an electric motor at oneend of and co-axial with said body, a tool-bit holder slidably mountedcoaxially with and in theother end of said body, said motor having ashaft extending co-axially within'said body, a bearing between the endof said shaft and said tool-bit holder, and a striker mounted on andconstrained to rotate with said shaft and reciprocable within said bodyfor cooperation with said tool-bit h'older, said striker havingcentrifugal rolling elements constrained to rotate with it and movableat least in part radially with respect to said axis while co-operatingwith the interior surface of said body, said interior surface dvergingfrom the end nearer to said motorand merging into a portion havinggrooved helical paths so disposed as to co-operate with said rollingelements when said striker is impacting said tool-bit holder, the handof said helical paths being opposite to that of th'e paths traced bysaid rolling elements while said striker approaches said tool-bitholder.

8. A percussion tool including a tub-ular body, a rotary driving member,a striker in said body coeaxial with and constrained to rotate with saiddriving member and reciprocable along the axis of rotation of saidmember, said striker comprising centrifugal masses constrained to rotateand reciprocate with it but movable at least in part radially withrespect to said axis, an abutment member slidably carried in said bodyco-axially with said striker for co-operation with said striker, theinterior surface of said body providing an idling track for said masseswhen said striker is in contact with said abutment member and when saidabutment member'is extended, and said interior surface also havingshallow helical grooves on the side of said idling track remote fromsaid striker for co-operation with said masses so as to accelerate saidstriker in the direction away from said abutment member, and means insaid body co-operating with said striker to reverse the direction of itstranslatory motion when` said striker is remote from said abutmentmember.

9. A percussion tool including a tubular body,l

a rotary driving member, a striker in said body co-axial with andconstrained to rotate with said driving member and reciprocable alongthe axis of rotation of said member, said striker comprising centrifugalmasses constrained to rotate and reciprocate with it but movable atleast in part radially with respect to said axis, an abutment memberslidably carried in said body coaxially with said striker forco-operation with said striker, the interior surface of said body havingrstly an idling track for said masses when said striker is in contactwith said abutment member and when said abutment member is extended,secondly shallow helical grooves on the side of said idling track remotefrom said striker for co-operation with said masses so as to acceleratesaid striker in the direction away from said abutment member and thirdlya sinuous circumferential groove between said helical grooves and saididling track and placed to receive said masses on retraction of saidabutment member, and means in said body co-operating with said strikerto reverse the direction of its translatory motion when said striker isremote fromV said abutment member.

10. A percussion tool including a rotary driving member, a strikerco-axial with and constrained to rotate with saiddriving member andreciprocable along the axis of rotation of said member, a tubular raceco-axial with said driving member and having h'elical paths on itsinterior surface, saidstriker comprising centrifugal masses constrainedto rotate and reciprocate with it and capable vof moving at least inpart radially with respect to said axis while co-operating with saidinterior surface, an abutment member for cooperation with said strikerwhile it is in a position such that said masses are traversing saidhelical paths, and means for reversing the direction of translatorymotion of said striker while it is remote from said abutment member, theshape of said interior surfacebeing such that cross sections thereoftaken in succession in the direction towards said abutment member areovals of approximately elliptical form, of which the ratio of major axisto minor axis increases in said direction, while the major axis of theoval at any section is angularly displaced about said axis, in thedirection opposite to the direction of rotation of said driving member,with respect to' the major axis ofthe oval at any section more remotefrom said abutment member.

11. A percussion tool including a tubular body, a driving shaftsubstantially co-axial with said body, a centrifugal mass constrained torotate with said shaft but movable parallel and radially with respect tothe axis of said shaft, said body having on its interior surface ahelical groove with which' said mass co-operates'under the influence ofcentrifugal force to produce any axial thrust, means on said body for'taking the momentum of said mass in one axial direction and means forreversing the direction of. translatory motion of said mass after its.displacement in the other axial direction, the shapes of said mass andsaid groove being'such that the dynamic coupling between them is higherwhen the helical path of the mass is of the same hand as said helicalgroove than when the helical path of the mass is of the opposite hand tothe helical groove.

12. A percussion tool including a tubular body,

a driving shaft substantially co-axial 'with said body, a centrifugalmass constrained to rotate with said shaft but movable parallel andradially with respect to the axis of said shaft, said body having on itsinterior surface a helical groove with' which said mass co-operatesunder the influence of centrifugal force to produce an axial thrust, anda frusto-conical portion having its larger end adjacent to said groove,the shapes of said mass and said groove being such that the dynamiccoupling between them is higher when the helical path of the mass is ofthe same hand as said helical groove than when th'e helical path of themass is of the opposite hand to the heli-cal groove, and such higherdynamic coupling producing on said mass a thrust in the axial directionopposite to that produced on said mass by said frusto-conical portion.

13. A percussion tool including a tubular body, a driving shaftsubstantially co-axial with said body, a centrifugal mass constrained torotate with said shaft but movable parallel and radially withrespect tothe axis of said shaft, said body having on its interior surface ahelical groove with which said mass co-operates under the inuence ofcentrifugal force to produce an axial thrust, a frusto-conical portionhaving its larger end adjacent to said groove,'and a cylindrical portionon the side of said groove remote from said frusto-conical portion, theshapes of said mass and said groove being such that the dynamic couplingbetween them is higher when the helical path of the mass is of the samehand as said helical groove than when the helical path of the mass is ofthe opposite hand to the helical groove, and such higher dynamiccoupling producing on said mass a thrust in the axial direction oppositeto that produced on said mass by said frusto-conical portion.

14. In a percussion tool, a tubular body, a rotatable striker Withinsaid body and capable of translation along the axis thereof a motordrivably connected to said striker, said striker including a centrifugalmass constrained to follow the rotation and translation of said strikerand capable of bearing under the inuence of centrifugal force on theinterior surface of said body, at least part of said surface having ahelical form such as to cause a screwing effect by which part of therotary motion of said striker is converted into translatory motion in anaxial direction, and means for reversing the said translatory motion ofthe striker, so that undel` the alternating effects of said helicalsurface and said reversing means said striker will reciprocatecontinuously.

RUDOLF GOLDSCHMIDT.

